1. Technical Field
The present invention relates to a surface emitting laser, and more particularly, to a surface emitting laser including a current confinement layer that confines a current path through which current flows between electrodes.
2. Related Art
The current confinement layer includes an oxidized insulating layer obtained by selectively oxidizing compound semiconductor including aluminum, such as AlAs, and an opening portion made of the compound semiconductor including aluminum in which a high current (carrier) density is obtained by the oxidized insulating layer.
To increase current input efficiency in such a semiconductor laser device, one idea is to provide, on both sides of the current confinement layer, graded-composition layers of AlGaAs in which the aluminum composition ratio gradually decreases as a distance from the surface of the current confinement layer increases.
Japanese Patent Application Laid-open No. 2002-359434, for example, describes a surface emitting laser device in which AlGaAs graded-composition layers are disposed on both sides of an AlAs layer. In each AlGaAs graded-composition layer, the aluminum composition ratio decreases continuously until reaching Al0.15Ga0.85As, which is the material of the AlAs cavity spacer layer.
The inventors of the present invention used such techniques to manufacture a semiconductor laser device that includes AlGaAs graded-composition layers on both sides of a current confinement layer. However, when manufacturing the device, because it was difficult to control the oxidation of regions near the interfaces between oxidized regions of the current confinement layer and the AlGaAs graded-composition layers, peeling of the layers occurred near the oxidized regions, resulting in poor yield. When the current confinement layer was near the active layer, the unevenness of the oxidation penetration at the interfaces between the oxidized regions and the non-oxidized regions made it impossible to obtain an active layer with uniform characteristics. In addition, dislocations caused by strain occurred in the active layers, further decreasing the yield. Even if there were no problems during manufacturing, the resulting devices had poor long-time reliability.
The present invention has been achieved in view of the above aspects, and it is an object of the present invention to improve yield when manufacturing surface emitting laser devices and to provide a surface emitting laser device that has excellent long-time reliability.